Figure 5. Illustrating the concept of a dose–volume constraint in inverse planning. The figure shows an integral (sometimes called cumulative) dose–volume histogram for an organ at risk (OR). The clinician specified the starred points as dose–volume constraints and the algorithm "did its best" to meet them (not entirely succeeding as not all the stars are to the right of the curve). For example, 0.85 of the OR volume receives 20 Gy or more; 0.3 of the volume receives 27 Gy or more and so on.